We have determined the entire mRNA sequence of human liver apolipoprotein (apo) B-100, the ligand on low density lipoproteins (LDL) which interacts with the LDL receptor and initiates receptor mediated endocytosis and LDL catabolism. At 4536 amino acids, apoB-100 is the largest protein cloned and sequenced. The availability of cDNA clones have enabled us to: 1. Predict a low amphipathic helical structure of apoB-100, an unusual feature when compared to other human apolipoproteins. 2. Propose multiple LDL receptor binding domains in apoB-100. 3. Localize the apoB-100 gene to the p23 pter region of human chromosome 2. 4. Determined there is one gene copy per haploid genome. 5. Analyze genetic defects in apoB structure in patients with dyslipoproteinemias such as familial abetalipoproteinemia and hypobetalipoproteinemia. 6. Study the expression of the apoB-100 gene in vitro. 7. To determine structural relationship between apoB-100 and apoB-48. We have also initiated studies on the regulation of human apoA-I gene. We have determined the region between the cap site and 560 bps 5' upstream contain all the information required for tissue specific expression of apoA-I by way of CAT assay of transient expression of transfected apoA-I promoter constructs. The methodologies will be applied to normal as well as abnormal apolipoprotein genes.